1. Field of the Invention
This invention relates, in general, to the preparation of a hot coffee beverage, and in particular, to the preparation of an espresso-type coffee beverage without the use of conventional espresso machines.
2. Description of Related Art
Coffee beverage comprises an aqueous solution of the water-soluble (and sometimes insoluble) constituents of the roasted and ground beans of the tree of the family, Rubiaciae. There are many varieties of this plant, but the only two which have any commercial significance are Caffea arabica, and increasingly, Caffea canephora ("robusta").
Almost universally, the extract is brewed by contacting the roasted and ground coffee with hot water at a temperature from moderately below boiling to moderately above, for a predetermined brewing time, separating the extract, including the solutes, from the insolubles, and consuming the resulting beverage. (Sivetz, M. and Desrosier, N. W., Coffee Technology, AVI Publishing Co., 1979; Clifford, M. N., and Wilson, K. C. (eds.), Coffee Botany, Biochemistry and Production of Beans and Beverage, AVI Publishing Co., Inc., pp, 251-284, 1985.)
Additionally, there are a number of ways that liquid coffee extracts and concentrates intended to be held for a period of time under refrigeration may be brewed. For example, U.S. Pat. No. 3,536,496 to Paolini describes a method for making a liquid concentrate of U.S.-type coffee by a drip method using boiling water in a ratio of 4 cups coffee to 8 cups water, to be stored under refrigeration and later diluted with boiling water in a ratio of 7:1.
In U.S. Pat. No. 1,891,383 to Giffen, et al., a method is described for making a liquid coffee concentrate of U.S.-type coffee using water at 30.degree.-50.degree. F. (45.degree. F. preferred) in a series of successive infusions of coffee at a ratio of about 1:1 by weight to form a concentrate having a specific gravity of 1.140.
In U.S. Pat. No. 2,338,608 to Weisberg, et al., a method is described for preparing a concentrate of coffee using water at 60.degree.-100.degree. C., which is successively percolated through a series of leaching units containing roast and ground coffee to produce extracts having a specific gravity 1.0025 and upward for subsequent refrigerated storage at from just below the freezing point of the extract to 60.degree. F.
Brewing methods can generally be categorized in three broad groups: (1) single-pass infusions in which the water is percolated or pumped through the roasted and ground coffee (which may partially serve as its own filter), then filtered through a metal, paper or cloth sieve; (2) percolation methods which recycle the extract through one or more volumes of grind consecutively, in either a co-current or counter-current flow, before the extract is siphoned off at the requisite strength; and (3) batch-slurry methods in which a fixed volume of coffee is mixed with a fixed volume of water is a brewing vessel, permitted to steep with or without agitation, then filtered or mechanically separated to produce the extract.
Espresso (or expresso) coffee beverage is a type which has found wide acceptance abroad, both in Europe and in Latin America. (See, Sivetz, M., Coffee Origin & Use, Sivetz Coffee Inc., 1977, Rev. 1978 & 1984.)
Espresso-type coffee typically comprises the dark-roasted beans, ranging from the dark, Viennese roast (15-16% moisture weight loss), to the French-type roast (17-18% moisture weight loss) and very black beans, to the Italian-type roast (19-20% or more moisture weight loss), which have a distinct, almost-burnt appearance and smell, with droplets of coffee oil formed on the surface of the beans. These darkly-roasted beans have considerably less acidity, aldehydes and aromas, are more brittle (and hence, subject to finer grinding and higher extraction rates), and have a higher fatty acid content than the lighter roasts.
Espresso coffee extract is produced by a positive displacement of a fixed quantity of water under pressure, usually by piston displacement, at super-heated temperatures (approx. 225.degree. F.) through a closely-measured (20 ml., 8 g.), packed bed of very-finely ground (300-400 microns) blend of espresso-type roasted beans contained in a chamber called a "porter filter" about 1 cm. high and 5 cm. in diameter (1 cup serving), having a very fine filter on the output side of the chamber. The cofee-to-water ratio is 3:1 by volume and 6-8:1 by weight. The 60 ml. (2 fl. oz.) charge of water passes through the grinds in a total extraction time of 1-4 seconds, yet produces a 1 fl. oz. serving of extract (typically served in a 1-3 fl. oz. demitasse cup), having a 3-4% solubles concentration with a 25% solubles yield and without exhaustive extraction. Espresso beverage prepared in the conventional manner will have an end temperature of about 150.degree. F. by reason of cooling contact between the hot water and the cold grounds and brewing chamber. Since this is very nearly at serving temperature, it is customary for some operators to "preheat" the porter filter and the serving cups to prevent the beverage from cooling too much. The beverage thus produced contains large amounts of colloidal matter and a small amount of insolubles, and has a dark, rich flavor and appearance which is accompanied by a head of lighter-colored froth, the so-called "creme-de-cafe" demanded by espresso beverage devotees. The beverage is intended to be consumed immediately with no holding time or reheating.
This is by contrast to American-style coffee extracts which, when brewed under recommended "ideal" conditions, is made by percolating a quantity of hot water (185.degree.-205.degree. F.) through a bed of relatively coarsely-ground (720-1200 microns), lightly-roasted coffee contained in an open field in a filter basket or a filter-paper cone in a water-to-coffee ratio of about 1.9-2.5 gal./lb., for a time period between 2-7 minutes (depending upon grind size) to produce 6-40 servings of between 5-7 fl. oz. each (typically served in 6-8 oz. cups or mugs), at a 1.15 to 1.35% solubles concentration, with an 18-22% solubles yield, but which may include exhaustive extraction. The beverage contains less colloidal matter, no insolubles (desirably), is lighter in color, aroma and texture, and contains no froth. It is intended either to be consumed immediately or held at serving temperature for periods of one hour or more.
Thus, the time/temperature exposure of the espresso coffee beverage is in the ratio of 1:100 to that for American-style extracts. Hence, the name "Espresso" carries with it several connotations, viz., a beverage that is brewed "quickly", a beverage that is brewed by "removing the essential part", and a beverage that is made "expressly", i.e., contemporaneously, in small individual servings for the consumer.
The key to producing a consistently high-quality espresso beverage (in addition to maintaining quality of beans, blend and roast), lies in maintaining a close control over the brewing process. Given the small quantities involved in the preparation of the individual-sized servings and the very short, time/temperature exposure of the coffee to water, a very small latitude for error in brewing is presented, relative to U.S.-style extracts. Thus, only a slight variation in any of the above brewing factors can result in a beverage that is either disagreeably weak or harshly bitter and astringent, with a resultant consumer rejection reaction that is proportionately stronger than to badly-brewed U.S.-style extracts.
Consequently, espresso brewing machines tend to be relatively large, complicated and expensive. Although there is a simple, range-type, two-chamber pressure-brewer called a "machinetta" for preparing small quantities of extracts made in the home, it does not permit the requisite degree of control to be exercised over the brewing operation as does the larger, automated, commercial machines, nor is the extract produced as consistently frothy as with the latter. The larger machines typically are sized in terms of the volume of the pressurized hot-water tank, as well as the number of brewing stations, or dispensing heads, each containing its own so-called "porter filter" to make either one or two cups of extract, although very large machines capable of brewing 1-2 liters at a time are known.
These machines are typically provided with a steam dispenser for heating and scalding milk which is added to the espresso extract to form a beverage called "Cappuccino".
These machines tend to be very large and expensive. While a small, portable, one-or two-cup machine for the home may be had for a few hundred dollars, even the smallest of restaurant or commercial espresso machines will occupy several cubic feet in volume and cost in the range of $1,000-$3,000, and very large machines can cost as much as $5,000 and take up a whole wall of a room, all representing a significant space and capital investment for a small establishment wishing to serve a quality espresso beverage.
Another problem with the machines is their complexity. A considerable degree of control is required over the very short brewing time and the higher pressures, temperatures, and volumes of water delivered to the grinds, requiring relatively precise adjustments, and the mechanization of which leads to high maintenance requirements and increased probability to breakdowns and/or downtime for the machine. Related to this is the fact that these machines, for the most part, are manufactured in foreign countries; hence, parts and service can be problematical.
Another problem is that they tend to be both labor- and time-intensive. As indicated, extracts are typically prepared on a one-or-two cup basis, at the most, and involves the grinding of the beans, the loading and tamping of the grinds in the porter filter, the locking of the porter filter to the machine and the activation of the lever or switch to begin the charge of metered water flowing through the grind. This tends to be time-consuming and can present a bottleneck for the household or small establishment having, say, 4-12 guests in a party who all wish to be served simultaneously with their beverage. This problem is multiplied for large establishments. This, in turn, tends to require a relatively skilled operator whose services can almost of necessity be exclusively dedicated to the day-to-day preparation, loading, maintenance and operation of the machines. (For a discussion of some of the specialized knowledge required of the potential purchaser/operator of smaller machines available, see, "Profits under Pressure: Espresso/Cappucino Machines", Gourmet Retailer; Miami, Fla., pp. 16.div.37, Nov. 1983).
Much of the recent technical art in the espresso field has thus been devoted to apparatus designed to overcome some of the above problems. See, e.g., U.S. Pat. No. 4,405,191 to Longo for an improved dispensing unit for espresso extract which is said to overcome water metering problems; U.S. Pat. No. 4,484,515 to Illy for an automatic espresso coffee machine utilizing pre-loaded coffee pods and microprocessor technology; and U.S. Pat. No. 4,151,626 to Berthelia for an apparatus for cleaning the cup-shaped filters associated with espresso machines.
It is by reason of the foregoing problems that many households and small restaurants forego having an espresso machine on the premises altogether.